1. Field of the Invention
The present invention relates to the field of cleaning of a substrate surface and more particularly to the area of chemical cleaning of a semiconductor wafer.
2. Discussion of Related Art
In semiconductor wafer substrate (wafer) cleaning, particle removal is essential. Particles can be removed by chemical means or by mechanical means. In current state of the art, particles are usually removed by both a combination of mechanical means and chemical means. “HF-Last” (a last hydrofluoric acid etch) processing poses distinct problems to the process engineer such as how to produce a particle-free hydrophobic bare silicon wafer at sub-0.10 micron line widths, while also being able to produce a completely watermark-free “mix-surface” patterned wafer. The mixed surface identifies both hydrophilic oxides as well as hydrophobic bare silicon on the same wafer. While one process may work well for one, it may not work well for both.
Watermarks are among the most common contamination problems found in LSI wet processing today, principally attributed to post HF rinsing and drying processes where both hydrophobic and hydrophilic surface states exist on the wafer. Hence, some of the main concerns driving the development of HF-last wafer processing equipment are, the elimination of watermarks, the reduction of the undesired surface reactions, such as, oxide growth, and a neutral particle contamination capability at or below 0.10 micrometers (μm). Watermarks are contamination formations, typically hydrated silicon-oxides, that appear after the drying of post-HF etched and rinsed, wet processed patterned wafers where both hydrophilic silicon oxides and hydrophobic silicon surfaces exist.
So far, mechanical agitation in a single wafer cleaning method has been achieved in several ways. At first, when wafers are completely flat, brushes can be used to scrub the wafer surface. However, this method is not possible when the wafers have any topography (patterns) that can be damaged by the brushes. Moreover, the brushes don't reach in between the wafer patterns.
Contamination left on the device side can cause a malfunctioning device. Contamination left on the non-device side (backside) can cause a number of problems. Backside contamination can cause the photolithography step on the front side to be out of focus. Contamination on the backside can cause contamination of the processing tools, which in turn can be transferred to the front side of the wafer. Finally, metallic contamination on the backside, when deposited before a high temperature operation, can diffuse through the silicon wafer and end up on the device side of the wafer causing a malfunctioning of the device.